1. Field of the Invention
Aspects of the present invention relate to a medium registration apparatus and an image forming apparatus including the same.
2. Description of the Related Art
In an image forming apparatus, it is important to register (align) inclined or misaligned printing medium, to form an image on a predetermined area of the printing medium.
Medium registration apparatuses may be classified as a center registration apparatus and as a side registration apparatus. As shown in FIG. 1, in a common center registration type, a leading edge T, of an askew piece of medium P, for example a piece of paper, is bumped to rollers R disposed on a rotating shaft X. The shaft is transversely disposed with respect to a medium transferring direction A, to thereby register the medium P.
As shown in FIG. 2, in a side registration apparatus, a guide G is disposed parallel to the medium transferring direction A. The askew medium P is moved in a direction B towards the guide G, and a side S of the medium P is bumped to the guide G, to thereby register the medium.
As shown in FIG. 3, a conventional double-sided image forming apparatus 1 comprises a single-sided printing path (SP) and a double-sided printing path (DP). Disposed on the single-sided printing path SP are a pick up roller 2, a registration roller 3, a photosensitive drum 4, a transfer roller 5, and a fixing device 6. The medium passing through the single-sided printing path S is aligned with a center registration, registration roller 3.
A reverse roller 7 is rotated in a reverse direction to move a single-side printed medium to the double-sided printing path (DP), in order to print on a second side of the medium. A side registration medium registration apparatus 10 is installed in the double-sided printing path (DP). The medium registration apparatus 10 comprises a first guide plate 11 that guides the single-sided printed medium toward the double-sided printing path (DP), and a second guide plate 13 that faces the first guide plate 11. A space, separating the first guide plate 11 and the second guide plate 13, forms a path through which the medium is transferred during the double-sided printing process.
As shown in FIG. 6, idle rollers 12 are disposed on one side of the first guide plate 11 to move an askew medium toward a side guide 15.
As shown in FIGS. 4 and 5, the second guide plate 13 comprises a side guide 15 that functions as a side registration reference line L for medium. Also, as shown in FIG. 4, on a side edge of the second guide plate 13 duplex rollers 14 are provided, which transfer medium to the single-side transferring roller 8, along the double-sided printing path DP. The duplex rollers 14 are provided in opposition to the side guide 15, to rotate the idle rollers 12. In general, rotating shafts 12a of the idle rollers 12 are offset at an angle of about 6°, with respect to rotating shafts 14a of the duplex rollers 14.
A medium that enters the double-side printing path DP is transferred in a skewed direction with respect to the medium transferring direction (see A in FIG. 4), by the duplex rollers 14 and the idle rollers 12, and one side of the medium is bumped to the side guide 15, to be side registered. The registered medium reenters the single-sided printing path SP, due to the rotation of the single-side printing transfer roller 8.
The medium registration apparatus 10 has shorter shafts and needs fewer components than a center registration apparatus, has a lower cost, and does not require rotating shafts disposed across the entire medium.
The medium registration apparatus 10 is usually set to be suitable for A4 size medium (210×297 mm). However, if a user wants to double sided print on A5 size medium (148×210 mm) or B5 size medium (182×257 mm), it is impossible to side register. As shown in FIG. 4, since a large gap W is between the side S1 of the A5 medium and the side guide 15, the side S1, of the A5 medium is not bumped to the side guide 15, even if the A5 medium passes through the double-sided printing path DP that is set for the A4 medium.
If the double-sided printing path DP is made longer, so that the side S1 of the A5 medium can be bumped to the side guide 15, the size of an image forming apparatus must be increased, thereby decreasing the space efficiency of the imaging forming apparatus.